A lock mechanism for locking a casement window, wherein a pivotable sash containing a pane of glass is to be closed against a window frame, typically includes one or more locking rods or lockbars that are laterally movable between a retracted and extended position for inserting and removing an outer end of the bar into and out of engagement with the sash.
Some lock mechanisms may include a laterally movable or rotatable handle or knob directly coupled to the inner end of the lockbar for moving the lockbar between the extended and retracted positions as the handle is slid or rotated. The direct coupling between the lockbar inner end and the knob or handle typically has the end of the lockbar rotatably pinned to the handle. In other direct coupling lock mechanisms, an intermediate link may be placed where one end is pinned to the lockbar and the other end is pinned to the handle or knob.
A possible disadvantage of the prior art lies in the direct mechanical linkage, which can often be difficult to extend and retract because of inherent friction or resistance in the mechanical linkages. Many of the mechanical linkages over time may change angular orientation with respect to the handle or knob as it is rotated, resulting in relatively large and varying rotational forces to be applied to the handle or knob to affect the extension or retraction. The magnitude and varying nature of the operational force sometimes result in jerky operation and perhaps a very high initial force. The combination of these effects can often lead to difficulty in operating the window lock and possibly failure of the window lock.
Other lock mechanisms may include lockbars along an edge of a window frame to lock a sash against the frame. The lockbars typically have a plurality of rollers mounted on the lockbar that engage ramped keepers spaced along the edge of the window sash. The rollers and keepers are usually spaced so that the rollers engage the keepers in a sequential manner, starting from the bottom of the sash and ending with the top of the sash. As a result, the bottom of the sash is normally locked first and the sequential interaction of the middle and top rollers with the middle and top keepers respectively results in the middle and top portions of the sash being pulled against the frame and locked shut.
However, these locking mechanisms may be difficult to install because the spacing between the handle or actuator from the tie bar can vary depending upon the manufacturer and window style. As a result, some locks are usable only with certain styles of windows and other window styles require that locks be specifically manufactured for that style. Therefore, manufacturing costs can be quite high and the wide variety of locks that are required requires builders to maintain undesirably large inventories of such locks.
What is desired, therefore, is a lock mechanism for a casement window that can easily be installed on a variety of window designs. Another desire is a lock mechanism that is easy to operate by a user without expending an inordinate amount of energy by the user.